Sent my 63FZ in to YS service last month because it would'nt hold pressure & was leaking fuel. cleaned the regulator & tried adjusting with no improvement. Sent it in to YS service & they said they replaced some pump parts & did a piston upgrade. Got my engine back with the old regulator parts they replaced but my engine is no different than before. Will not hold pressure, I have run this engine before in a couple of my other planes so it's not like I don't know how to setup the plumbing on this engine. I thought YS sevice ran these engines before shipping them back, I have'nt touched the regulator figuring that if they ran it before sending it back it should run for me. As it is now the fuel leaks through the carburator when cranking it over. If I crank it over long enough to build some pressure it leaks fuel all over the place, then I can turn the prop slowly by hand & hear the pressure escaping through the carb. When I release the pressure from the tank I get very little or no hissing at all.[]